A typical motor vehicle air conditioning system includes a compressor, a condenser, an expansion device, and an evaporator. The condenser is disposed in the front portion of the engine compartment or more precisely, in front of the radiator exposed to the outside ambient air. The evaporator is disposed within a heating, ventilating, and air conditioning (HVAC) module that conditions and distributes air to the passenger compartment of the motor vehicle. Hydraulically connecting the aforementioned components are series of refrigerant tubes that are capable of conveying a two phase refrigerant operating under high and low pressure flows. The compressor is commonly referred to as the heart of the air conditioning system in which it is responsible for compressing and transferring the refrigerant throughout the system. Heat energy from the passenger cabin is absorbed by the refrigerant flowing through the evaporator. The compressor then transfers the refrigerant to the condenser where the heat energy is dispelled to the ambient air outside of the vehicle.
CFC-12 and other chlorofluorocarbon (CFC) refrigerants have been widely used in motor vehicle conditioning systems for over 30 years. The CFC refrigerants, having a vapor density less that air, rise to the stratosphere where the halogen atoms of the CFC react with the ozone, thereby breaking down the protective ozone layer. As a result, over 190 countries have signed a treaty, called the Montreal Protocol, which calls for the ending of the production of CFC refrigerants for air conditioning and refrigeration uses on Dec. 31, 1995.
The United States Environmental Protection Agency (EPA) has determined several alternative refrigerants that are acceptable for use as a CFC refrigerant replacement in motor vehicle air conditioning systems, subject to certain use conditions. The decisions for these alternative refrigerants were based on their ozone-depleting, global warming, flammability, and toxicity characteristics. A number of these identified alternative refrigerants have a vapor density that is heavy than air. If a leak occurs in the air conditioning system within the hood of the motor vehicle, the heavier refrigerant vapor would settle to the lowest point within the engine compartment and dissipates to the environment. However, if a leak occurred within the evaporator or a portion of the refrigerant line that is contained within the HVAC module, the heavier vapors could potentially be dispersed into the passenger compartment.
U.S. Pat. No. 6,907,748 discloses a refrigerant leak detector positioned within the passenger compartment or within the HVAC module downstream of the evaporator as part of a system for the detection and venting of refrigerant leaks. If the refrigerant sensor was positioned within the passenger compartment, the sensor would be dependent on the blower to convey the leaked refrigerant to the sensor. For small leaks, the large amount of air flow may dilute the concentration of the refrigerant vapor below the detectable threshold of the refrigerant sensor. If the refrigerant sensor was positioned within the HVAC module and sensor failure occurs, the entire module would need to be disassembled to repair or replace the sensor. Furthermore, if a heavier than air refrigerant is utilized, any leaks would settle and collect in a low-lying area of the HVAC module and avoid detection until enough refrigerant is leaked to overfill the low-lying area.
There is a need to have a refrigerant detection system that can detect refrigerants having a vapor density heavier than air. There is a further need to have a refrigerant leak detection system in which the refrigerant leak detection sensor is readily accessible for servicing. There is a still a further need for a refrigerant leak detection system that can monitor for refrigerant leaks during periods when the blower is not in operation.